A similarity transformation for subcooled mixed convection film boiling in a porous medium

The classical two-phase boundary layer concept was adopted to analyse the problem of combined free and forced convection film boiling over an impermeable wall embedded in a porous medium. The governing equations, namely, the equations of continuity, energy and Darcy's model, were written for both vapor and liquid layers, and were solved simultaneously by means of the similarity transformation. Similarity solutions are found for a vertical flat plate, a horizontal circular cylinder and a sphere. Numerical integrations were carried out for given sets of the parameters associated with the vapor superheating Sup, the liquid subcooling Sub, the vapor mass flow rate R and the ratio of the liquid Rayleigh number to Peclet number Ra_xf/Pe_xf. It is found that a significant simplification of the problem is possible by setting the liquid stream function at the interface to zero. This simplification also reveals that the solution of the problem virtually depends on only three parameters, namely, Sup, Ra_xf/Pe_xf and the lumped parameter Sub/R.